1. Field of the Invention
The invention relates to processes for controlling the electrode of a direct current arc furnace, and more specifically to electrical control systems for adjusting the distance between the electrode and the melting bath of the arc furnace.
2. Background
An arc furnace with a DC supply that is controlled by two control circuits is disclosed in EP-B1-0,068,180. A current controller ensures a constant current corresponding to a prescribed desired current value. An electrode control circuit influences the position of the electrode, and thus the arc length. In the event of lengthening of the arc, the current controller must increase the voltage or drive the rectifier so that the current remains constant. However, this works only as long as there is a voltage reserve present. The control of the electrode is performed by an adaptable DC controller. The arc voltage, which is fed via an attenuator to a comparator or summer, serves as the actual DC voltage value. The desired DC voltage value must be calculated in each case taking into account the transformer voltage ratio and the electrode current for each operating point. It is initially limited by a limiter, in accordance with the transformer ratio of the converter transformer, and thus with the possible voltage range of the converter, such that the converter is operated in a steady state at just below the rectifier limit. The desired value is fed smoothed to the summer, so not to overshoot of the actual value in the case of sudden changes in the desired voltage value, which could cause interruption of the arc.